Heretofore, artificial leather made of nonwoven cloth which is impregnated with a polyurethane resin has been known for excellent feel. Such artificial leather has conventionally been produced, for example, by a wet process of impregnating nonwoven cloth made of ultrafine fibers with a polyurethane resin dissolved in an organic solvent such as N,N-dimethyl formamide (DMF), and removing the organic solvent by extraction in water.
In recent years, from the viewpoint of environmental burden, it has been desired to reduce the use of organic solvents, and even in the production of artificial leather described above, an aqueous polyurethane resin is considered to be used instead of the polyurethane resin dissolved in DMF.
Hence, as a production method of artificial leather by using an aqueous polyurethane resin, for example, the following Patent Document 1 proposes a method for producing artificial leather including the steps of impregnating base cloth with a polyurethane dispersion, the polyurethane dispersion being obtained by emulsifying and dispersing a urethane prepolymer having an isocyanate group at its end using a nonionic surfactant having an HLB of 7 to 16 and then chain-extending the urethane prepolymer using a polyamine compound having two or more amino groups and/or imino groups; thereafter, immersing the base cloth in warm water of 40 to 100° C.; and then drying it.
Patent Document 1: Japanese Unexamined Patent Publication No. 2000-282372